Various techniques are currently used to determine the position and motion of a non-cooperative, but reflective, object while allowing a compatible receiver to determine its own position, orientation and motion. Current techniques for determining self-position, self-motion, and self-orientation primarily use an inertial guidance system, a satellite navigation system, or a combination of the two. Current techniques for determining the position and motion of a non-cooperative, but reflective, object primarily use radar systems.
An inertial guidance system provides the position, velocities, and attitude of a vehicle by measuring the accelerations and rotations applied to the system's inertial frame. A typical system will use angular accelerometers to measure how the vehicle is rotating in space (one sensor each for pitch, yaw, and roll), linear accelerometers to measure how the vehicle is moving in space (one sensor for each of the three axes), and include a gyroscopic element for maintaining an absolute positional reference. These measurements are combined to estimate acceleration, velocity, position, and attitude, starting from a known initial position. In general, inertial guidance systems suffer from an accumulation of measurement errors that result in progressively larger errors in velocity and position.
A satellite navigation system provides the position of a vehicle using signals transmitted from satellites. One satellite navigation system is the Global Positioning System (GPS). From the broadcast GPS satellite signals in view of a GPS receiver, a GPS receiver will determine its relative distance from the group of GPS satellites in space. GPS is not accurate enough for fine attitude (orientation) determination. Also, GPS signals may be jammed to prevent a GPS receiver from determining its position.
An inertial guidance system may be improved by incorporating a satellite navigation system. The satellite navigation system may be used to correct the accumulated measurement errors of the inertial guidance system. Neither of these navigation techniques, however, may be expanded to determine the position and motion of a non-cooperative, but reflective, object. Instead, an additional system is needed to accomplish this. A typical system would be a monostatic radar system. The radar system could be located onboard the vehicle or elsewhere. The radar system would transmit and receive radio waves reflected off the non-cooperative object. If the radar system were not located onboard the vehicle, then some means of communicating the information from the radar to the vehicle would be necessary.
A need exists for a way to determine the position and motion of a non-cooperative, but reflective, object that does not suffer from an accumulation of measurement errors, as with inertial guidance systems. A need also exists for a way to determine the position and motion of a non-cooperative, but reflective, object that does not require the transmission of signals from the vehicle, as with onboard radar systems. For a radar system that is not located onboard the vehicle, the radar search and track resources would significantly limit the number of vehicles and non-cooperative objects that could be tracked. A need also exists for a single system that is able to determine its own position, self-motion, and self-orientation while simultaneously determining the position and motion of a non-cooperative, but reflective, object.